1. Field of the Invention
Embodiments of the present invention generally relate to a method and apparatus for filtering images.
2. Description of the Related Art
Among various combination of source and destination standard and dimension, the most significant mode will be a transcoding from MPEG-2 HDTV to H.264 HDTV. To achieve low bitrate with the highest picture quality, artifacts are usually removed from original MPEG-2 reconstructed images. If there are artifacts in the image, H.264 encoder (in the transcoder) reproduces the artifacts. Even when the artifacts do not affect the picture quality, they consume a considerable number of bits.
In most cases, transcoded bitstreams are allowed to use much less number of bits than original bitstreams. Thus, the reproduction of the artifact is imperfect. It undesirably emphasizes the artifacts in the transcoded images. The artifacts also disturb motion re-estimation and intra prediction mode decision. Therefore, noise filtering is an indispensable step for high quality transcoding, which is often called mid-filter due to its location between a (MPEG-2) decoder and a (H.264) encoder. Dominant and typical types of MPEG-2 artifacts are ringing (also called mosquito noise in motion pictures) and deblocking noise.
Hence, artifacts should be removed for better subjective quality, as well as, high quality transcoding and better performance. However, the existing filters cannot show satisfactory performance on high-definition images.
Therefore, there is a need for an enhanced method and apparatus for dealing with artifacts in an image.